#include <stdio.h>

int main() {
    printf("请输入一个字符: ");
    char c = getchar();
    if (c >= 'A' && c <= 'Z') {
        c = c + ('a' - 'A');
    } else if (c >= 'a' && c <= 'z') {
        c = c - ('a' - 'A');
    }
    printf("转换后的字符: ");
    putchar(c);
    printf("\n");
    return 0;
}
